Misfire?

[Wounded_Fighter]

So leaving work today I went and started my MJ and she was acting like she was missing a beat with 2 of the cylinders, seemed worse when I was on the gas. 

 

I poked around under the hood to make sure injectors electrical were tight and all the spark plug wires were tightly secured as well. It didn't change anything. 

 

So I turned her off and waited 5 seconds then turned it over again. Ran normal. 

 

Thoughts? 

[Eagle]

Incipient CPS failure. I had that in an XJ (the original '88) a number of years ago. Had been running fine. Drove a few miles from a Subway restaurant down the road to Walmart. Noticed a skip under power on the highway, but no other issues. came out of Wally World and it was dead as a doornail.

 

Another possibility is failing spark plug wires but, with a Jeep 4.0L, I now tend to suspect the CPS before I look at ignition wires.

[Dzimm]

I'd agree with Eagle the CPS is always a high possibility on these engines. 

 

A good way to test each cylinder for a misfire is to start the engine up and one by one unplug the injectors and plug them back in.  When you unplug the injector, if the engine shakes worse and you can hear it start to misfire worse, then that cylinder is good.  When you have one that doesn't really affect the way the engine is moving and you can't hear a change in sound when unplugged, that cylinder is misfiring. 

[zomeizter]

Wouldn't an incipient CPS failure cause engine stalling instead of misfiring? Weak ignition wires and/or bad plugs is likely, I reckon it's time for a tune-up OP :)

[HOrnbrod]

On 7/5/2018 at 8:16 PM, Eagle said:

Incipient CPS failure. I had that in an XJ (the original '88) a number of years ago. Had been running fine. Drove a few miles from a Subway restaurant down the road to Walmart. Noticed a skip under power on the highway, but no other issues. came out of Wally World and it was dead as a doornail.

 

That's what you get for frequenting Wally World.  

[Wounded_Fighter]

2 hours ago, zomeizter said:

I reckon it's time for a tune-up OP :)

Maybe.. doesn't look like the wires or plugs have been messed with in quite a few years. I've only had her for about a month now. 

 

23 minutes ago, HOrnbrod said:

That's what you get for frequenting Wally World.  

Hah! This.

 

 

Thus far I did the refresh on the CPS connector, had to search fire it... no problems yet. Gonna do dist index before I go any further on the problem I suppose. If it comes back I'll look at CPS a little closer

 

Avoid the #partscannon 

[Eagle]

1 hour ago, HOrnbrod said:

 

That's what you get for frequenting Wally World.  

 

Mea culpa.

[rokinn]

42 minutes ago, Wounded_Fighter said:

Thus far I did the refresh on the CPS connector, had to search fire it... no problems yet. Gonna do dist index before I go any further on the problem I suppose. If it comes back I'll look at CPS a little closer

I recently replaced my CPS with a high altitude one (we're high here in CO, I'm talkin' altitude now) .  I had a mostly consistent stumble in my idle.  When I pulled the CPS it was so filthy I'm surprised the motor ran at all.  When I installed the new CPs it purred like a big ole cat.  Might be worth pulling it just to clean it and see what happens.